So you know how a rainbow is supposed to have every color in it? It doesn’t. And this video from The Royal Institution, in part, addresses why you won’t find purple in rainbows. But what the video is actually about, and what’s awesome, is how we perceive color.

Inside our eyeballs, along the back surface, we have rod and cone-shaped cells that form the retina. When the cone cells of the retina are excited by light pouring in through the pupil, they send electrical signals to the brain. And we perceive specific colors based on what mix of signals are sent to the brain. The cones in humans are normally only sensitive to three colors: red, blue and green because the three types of cones we have are sensitive to red, blue and green wavelengths of light. Some females can have additional cones that are sensitive to another wavelength of light thanks to a genetic anomaly. There is an excellent Radiolab episode about color which features a woman with tetrachromacy. She’s able to see colors that you and I just can’t. The episode also mentions that butterflies have five kinds of cones and that there are animals with as many as 16 different kinds of cones. They can see so many colors that we’ll never see. When you think about it, it seems unfair.

Still, color is amazing, and this short video is a great introduction to how we perceive it. It was produced by the Royal Institution of Great Britain, which has a bevy of fascinating science videos (like any of the Modern Alchemist series, although I particularly like the one about Iodine). This video is hosted by Steve Mould, and it asks a very basic question “How do our brains see the colour magenta which doesn’t have a wavelength?”